New
New
Year 10
AQA
Foundation

# Calculating energy changes (Ek and Ep)

I can use the principle of conservation of energy to calculate changes in energy of moving objects.

New
New
Year 10
AQA
Foundation

# Calculating energy changes (Ek and Ep)

I can use the principle of conservation of energy to calculate changes in energy of moving objects.

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## Lesson details

### Key learning points

1. Energy cannot be created or destroyed.
2. In an ideal situation, no energy is dissipated.
3. As an object changes height, change in gravitational potential energy = change in kinetic energy.

### Common misconception

Energy can be lost or created in physical processes.

Always discuss how energy is dissipated to the surroundings when discussing energy transformations, even when dealing with ‘ideal situations’ in which there is no dissipation.

### Keywords

• Conservation of energy - The principle of conservation of energy states that the total amount of energy at the end of a process is always the same as the total amount of energy at the beginning.

• Dissipate - Friction or air resistance can cause energy to dissipate into the surroundings as heat.

• Gravitational potential energy - The energy an object has in its gravitational store is referred to as the object’s gravitational potential energy.

• Kinetic energy - The energy an object has in its kinetic store is referred to as the object’s kinetic energy.

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Starter quiz

### 6 Questions

Q1.
Match each symbol in the equations \$\$E_p = mgh\$\$ and \$\$E_k = ½mv^2\$\$ with the quantity it represents.

gravitational potential energy

mass

gravitational field strength

height

kinetic energy

speed

Q2.
Match each quantity with its unit.

joule (J)

kilogram (kg)

metre per second (m/s)

Correct Answer:Gravitational field strength,newton per kilogram (N/kg)

newton per kilogram (N/kg)

metre (m)

Q3.
Which of these statements are correct?
Correct answer: The kinetic energy of an object is directly proportional to its mass.
The kinetic energy of an object is directly proportional to its speed.
Correct answer: Gravitational potential energy is directly proportional to an object's mass.
Gravitational potential energy is directly proportional to an object’s speed.
Q4.
An eagle with mass 4.0 kg flies at speed 15 m/s. How much energy is in its kinetic store?
30 J
60 J
240 J
900 J
Q5.
A book of mass 1.6 kg falls off a shelf onto the floor. The shelf is 2.0 m above the floor. What is the change in energy in the gravitational store? (Use \$\$g\$\$ = 10 N/kg.)
3.2 J
13.6 J
16 J
20 J
Q6.
An apple of mass 200 g falls from a branch that is 150 cm above the ground. What is the change in energy in the gravitational store? (Use \$\$g\$\$ = 10 N/kg.)
30 J
300 J
3000 J
300 000 J

## Exit quiz

### 6 Questions

Q1.
The principle of states that total amount of energy at the end of a process is always the same as the total amount of energy at the beginning.
Q2.
A rock on a cliff has 1600 J of energy in the gravitational store. It falls off the cliff onto the ground below. During the fall, no energy is dissipated. What is the energy transfer during the fall?
1600 J is transferred from the kinetic to the gravitational store.
Correct answer: 1600 J is transferred from the gravitational to the kinetic store.
Less than 1600 J is transferred from the gravitational to the kinetic store.
More than 1600 J is transferred from the gravitational to the kinetic store.
More than 1600 J is transferred from the kinetic to the gravitational store.
Q3.
A 0.20 kg ball is thrown straight upwards and reaches a maximum height of 2.1 m. The ball’s kinetic energy at the start is J. (Assume no energy is dissipated. Use \$\$g\$\$ = 10 N/kg.)
Correct Answer: 4.2, 4.20, 4.2J, 4.2 J, 4.20J
Q4.
A plate is dropped. If no energy is dissipated during the fall, the final speed of the plate before it hits the ground is 4 m/s. If energy is dissipated, which of these statements is correct?
Correct answer: The final speed will be less than 4 m/s.
The final speed will be 4 m/s.
The final speed will be more than 4 m/s.
It is impossible to say whether the final speed will be more or less than 4 m/s.
Q5.
A child sledges down a hill of height 12 m. The total mass of child and sledge is 30 kg. At the bottom, the kinetic energy is J. (Assume no energy is dissipated. Use \$\$g\$\$ = 10 N/kg.)
Correct Answer: 3600, 3600J, 3600 J, 3600joules, 3600 joules
Q6.
A mountain goat with mass 52 kg jumps straight upwards, leaving the ground at speed 6.0 m/s. The maximum height it can reach is m. (Use \$\$g\$\$ = 10 N/kg.)
Correct Answer: 1.8, 1.80, 1.8m, 1.8 m, 1.80m